In any system of switchable exterior electrical signaling lamps in which an operator of the switches at some dashboard cannot see the lamps from his location: a monitoring device is desirable which indicates dashboard whether each lamp is functioning properly.
If an electrical lamp conducts the proper current when impressed with proper potential difference, hereinafter the status of the lamp is termed "functional".
In the prior art a common way of indicating the lighting of a remote electrical lamp is to connect a pilot light in parallel with the lamp, so that the pilot light lights with and only with the application of a potential difference areas the parallel combination, e.g., the turn-signal dash indicators in a typical automobile. (See Chilton, op.cit., for a survey of automotive dash-indicator displays array). This type of indicator circuit does not indicate whether the lamp is functional, however.
In the vehicular application the most important exterior signaling lights are the turn-signal, brake, and tail lamps, because of safety. Yet the prior art has not yet fielded a device to my knowledge capable of definitely indicating the status of these lamps. The thermal turn signal flasher used from ca. 1950 to 1990 provided a clicking sound which indicated normal current through two incandescent lamps in parallel, and if one was not functional the clicking cadence was altered. (See A. Trantner, loc.cit. for a survey of flashers and circuits).
Since the primary application of the present invention is to the signaling system of an automobile, therefore consider the schematic diagram of FIG. 1 of an automobile signaling system of the prior art comprising a battery 1 for direct current (d.c.) electricity, a steering-column-mounted turn-signal switch assembly 9, having left detent, OFF, and right detent positions, front and rear, left and right external signaling lamps 2, 3, 24, & 25, parking lamp switch 6, left and right parking lamps 4 & 22, left and right tail lamps 5 & 23, a dashboard containing turn-signal indicator lights 7 & 21, turn-signal flasher 14, brake switch 10, hazard warning flasher 17 (with knob symbolized by 19), ignition net 13, and a system ground. (See also Ford Light Truck Shop Manual, loc.cit. for circuitry.) In FIG. 1 the turn-signal switch is shown in the left detent position, so that lamps 2 & 3 are flashing, and the closing of the brake switch 10 will cause right rear lamp 25 to shine steadily. The circles 8, 11, 12, 15, 16, 18, & 20 denote terminals of the turn-signal switch.